Changes in human vision throughout the lifespan are well documented, but the factors to which these changes can be attributed are not understood. Nor is it clear from current evidence how age-correlated changes at one level of processing are related to changes at other levels. The purpose of this research is to study some of the age changes that occur in color vision throughout the lifespan, with particular emphasis on the elderly (60-90 years). Test conditions will be used that allow the separation of prereceptoral, receptoral, and postreceptoral mechanisms. Prereceptoral factors that will be studied with psychophysical methods include the crystalline lens and macular pigment. These media selectively absorb the light that can reach the receptors modify the spectral distribution and intensity of the retinal stimulus. Receptoral mechanisms will be isolated by selective chromatic adaptation in order to measure (to a first approximation) the spectral sensitivity of the three classes of cone photoreceptor. Pseudophakic patients (having an intra-ocular lens implant) will also be studied to test the hypothesis that ultraviolet light exposure contributes to age-correlated changes in short-wave cone sensitivity. Preliminary data show selective damage to human short-wave cones when the intra-ocular lens transmits radiation between 300 and 400 nm, despite excellent visual acuity and no pathology evident on a standard ophthalmological examination. At the postreceptoral level, spectral sensitivity will be measured for the luminance channel (which receives a combined input from the middle- and long-wave cone) and the chromatic channels (which receive input through subtractive interactions of all three cone types). Postreceptoral chromatic processing will be further separated by measuring the wavelength loci of unique blue, green and yellow. The chromaticity coordinates of the spectral mixture that appears uniquely white will also be determined. Since all of these prereceptoral, receptoral and postreceptoral variables will be measured in the same 60 normal subjects and 25 pseudophakic subjects, it will be possible not only to document age-correlated changes in individual mechanisms, but also to test models of the relations between processing at different levels. This research is thus concerned with separating the optical and neural mechanisms that mediate age-correlated changes in the perception and processing of color. An understanding of these mechanisms and their relations may not only contribute to the study of vision, but also to the general study of aging in sensory-neural systems that mediate perception.